In general, undesirable noise such as isolated pixel data exists in an image that has been scanned in by a copier or a facsimile machine. To remove the noise by an image process such as a digital filtering process, the quality of an image is generally reduced. Japanese Patent Publication Hei 10-93824 discloses one example of the detection and correction of the isolated pixels based upon a preprocessing by a MTF filter for edge emphasis, a process using a number of pixels having a predetermined range of intensity and a reference table as well as a process of correcting only a current pixel. The above technology requires the reference table that must be prepared in advance. Furthermore, since the table referencing and the matrix calculation in the preprocessing by a filter consume a large amount of processing time, the processing speed has not improved.
To accomplish the above and other prior art image processing, a processor called a single program multiple data (SIMD) has been utilized. Since a SIMD processor carries our the same instruction on multiple data sets during a single cycle, the SIMD processor significantly improves efficiency of a certain process. While FIG. 1 illustrates how the SIMD processor processes the multiple data, FIG. 2 illustrates a conventional processor processes the same data in the same manner. In FIGS. 1 and 2, the both processors multiply the multiple data by two (×2) or shift the data to the left by one bit. The SIMD processor outputs the results from the multiple data in a single cycle. On the other hand, since the conventional processor processes one piece of input data at a time during a single cycle, it must require eight cycles to process the entire data.
For the image processing for removing undesirable pixels, the SIMD processor still requires operations that are similar to the conventional processor for sequential tasks. For the above reason, the isolated pixel removal cannot take advantage of the SIMD processor.
Furthermore, the prior art techniques generally remove an isolated portion only from the currently processed pixel position. Since the isolated portion usually includes a plurality of pixels, the above prior art techniques fail to provide an effective image correction. It is desired that the isolated portions be removed in a cluster including pixels surrounding the current pixel rather the current pixel alone as shown in FIG. 3.